A study of the bis(4-chlorophenyl) sulphide by Cl-35 nuclear quadrupole resonance and ab initio calculations

As an extension of previous works in sulphur-substituted biphenyls, a compl ete pulsed Cl-35 nuclear quadrupole resonance (NQR) study of the bis(4-chlo rophenyl) sulphide compound is presented. In order to characterize the stru ctural thermal behaviour of the solid phase. the NQR spectra and spin-latti ce relaxation times were recorded from 80 K to 330 K. In addition, ab initi o calculations at HF/3-21G* and 6-31G* levels were performed in order to ob tain information about the equilibrium geometry and the torsional potential of the Free bis(4-chlorophenyl) sulphide molecule. The NQR study results s how that the title compound presents a unique stable crystalline phase in t he scanned temperature range. This phase diagram contrasts notably with tho se observed at the same temperatures in bis(4-chlorophenyl) sulphone and bi s(4-chlorophenyl) sulphoxide, which show an incommensurate phase transition and two-phase coexistence, respectively. The narrow NQR line observed sugg ests that the Cl-35 atoms in the unit cell are in crystallographic equivale nt positions. Ab initio calculations for the free molecule show that the sy mmetry point group is C-2 and the dihedral angle is 60 degrees. The results are discussed and compared with the known information about the sulphone a nd sulphoxide derivatives. The effect of the interphenyl linking group is a lso discussed, in order to understand the evolution of the phase diagram in this group of compounds.